Generally, a crank for driving a chainwheel to rotate is separable from the chainwheel using a tool, so that the separated crank and chainwheel can be maintained or repaired. The tool is referred to as a crank puller. To use the crank puller, first use a hex wrench to loosen a crank bolt from an internally threaded hole on the crank, and then screw a front end of the crank puller into the threaded hole to enable separation of the crank from a crank axle, which supports the crank and is associated with the chainwheel.
Most of the commercially available crank pullers are of a fixed type. That is, the crank puller has a front socket with a fixed size to meet the size of the crank axle. There are two different sizes available for the front socket on the crank puller. One of the two front socket sizes has a larger outer diameter about 16 to 17 mm, and the other one has a smaller outer diameter about 10.5 mm, so that crank pullers with differently sized front sockets can be used to separate cranks with differently sized crank axles.
There is also a replaceable type crank puller with a replaceable front socket. Differently sized front sockets can be detachably fitted to the front end of the crank puller for use in separating cranks with differently sized crank axles, so that the crank puller has a wider range of application.
While the replaceable type crank puller can be applied to cranks with differently sized crank axles by replacing the front socket thereof, the replaceable front socket tends to rotate along with the crank axle when being pressed against the crank axle, and is therefore easily worn out. That is, the replaceable front socket for the replaceable type crank puller has shorter service life compared to the fixed front socket for the fixed type crank puller, and fails to satisfy the consumers.
On the other hand, since the fixed type crank puller has front socket with fixed outer diameter, a user often has to prepare two crank pullers with differently sized front sockets for use with cranks having differently sized crank axles. In the event the crank axle is changed to another one with a different diametrical size at a later time, the user would have to purchase another crank puller corresponding to the new crank axle size. This would no doubt increase the user's purchasing cost.
From the above explanation, it is understood the conventional crank pullers, including both the fixed type and the replaceable type crank puller, have observable disadvantages in the practical application thereof and therefore require improvement.